The present invention relates to a grinder for comminuting waste material.
A known such grinder is shown in U.S. Pat. 5,639,032. This grinder comprises a grinding unit formed by a grinding rotor driven by an electric motor and by a counter blade carried by a machine frame. The waste material to be comminuted is urged to the rotor by means of a box shaped pushing element driven by a hydraulic jack so as to move across the bottom wall of a hopper containing the material to be comminuted.
Such known grinders are useful in connection with waste material of short dimension. However, these grinders are less suitable in connection with long wastes like laths or residual long portions of chip board material as obtained in factories for furniture and the like.
For grinding such elongate wastes there are known in the market grinders, which include two high friction serrated feed cylinders which are vertically aligned and are arranged in front of the grinding unit so as to positively feed the laths or the like towards the grinding rotor by firmly engaging the upper and lower surface thereof.
However, such grinders using a roller pair feed mechanism can grasp a single lath or the like at a given time, only. Also the contact area between the feeding rollers and the piece of waste material is small.
Thus it is an object of the present invention to provide a grinder having a waste material feed unit which can also feed a plurality of waste material pieces and which warrants a good frictional contact of the feed unit to the pieces of waste material.
To this end the invention proposes a grinder for comminuting waste material comprising a frame structure, comprising a grinding rotor journalled in the frame structure, which includes a plurality of cutting tools, comprising a counter blade carried by the frame structure and cooperating with the grinding rotor, and comprising feed means to positively feed waste material to the grinding rotor, wherein the feed means comprise a lower feed conveyor and an upper feed conveyor which are vertically aligned and each comprise an endless transport element running on two spaced return rollers, a lower work run of the upper conveyor and an upper work run of the lower conveyor thus forming a moving wall feeding passage for the waste material to be comminuted.
Further advantageous improvements of the invention relate to the following:
The endless transport element comprises a plate chain. In such a grinder the feed means are of particularly robust and solid construction.
The plate chain comprises plate chain members each having a plate portion and forward and rear hinge portions. This geometry of the single plate chain links is advantageous in view of a compact structure and in view of low production costs, since a separate driving chain is not necessary. The plate chain members can be easily connected by chain pins to form an endless belt like transport means.
Cooperating hinge portions of adjacent plate chain members form a hinge rib of constant cross section. In such a grinder the inward side of the transport means is formed with a plurality of transverse ribs, each of which are partly formed by a given plate chain member and a succeeding or preceeding adjacent plate chain member. The continuous transverse ribs thus at the same time form driving ribs cooperating with a driven return roller.
The plate chain member has a high friction surface. This further improvement is advantageous in view of good frictional contact between the two feed conveyors and the surfaces of the waste material pieces.
In view of obtaining the same advantage in a different way the invention further proposes a grinder, wherein the high friction surface comprises a rib structure, as well as a grinder, wherein the high friction surface comprises at least one spike, as well as a grinder, wherein the high friction surface comprises a rubber coating.
A still further improvement of the invention is a grinder, wherein the return rollers are provided with recesses cooperating with projections formed on the inward surface of the associated transport element. Thus the a driving return roller can transfer high forces to a transport element having matingly equidistant driving ribs on the inward face thereof.
In view of the same effect the invention further proposes a grinder, wherein the return rollers are of polygonal cross section.
A further improvement of the invention is a grinder, wherein the return rollers comprise spaced end plates and shaft rigidly connecting the end plates. This improvement is advantageous in obtaining return rollers of great axial dimension and yet small mass.
A further improvement of the invention relates to a grinder wherein at least one of the conveyors comprises a subframe movably carried by the frame structure. In such a grinder the conveyors can be at least partly adjusted in vertical direction. This allows the grinder to comminute waste materials of varying vertical dimension.
Furthermore a grinder is proposed, wherein the downstream return roller of one of the conveyors is carried by the movable subframe so as to be adjustable in vertical direction. This construction of the grinder allows vertical adjustment of the height of the effective transport gap defined by the two conveyors in a particularly simple way. The drive motors associated to the movable conveyor or the movable conveyors can be located at the upstream return roller, which is at the same time the pivot axis of the subframe. Thus the drive motor of the conveyor need not be moved when the vertical position of the downstream end of the conveyor is adjusted. This allows automatic adjustment of the movable conveyor by the incoming waste material pieces overcoming the weight of the subframe and the components carried thereby (downstream return roller plus transport element).
In a further embodiment the movable subframe is pivotable about the axis of the upstream return roller of the movable conveyor. In such a grinder no complicated guide means need to be provided for the downstream return roller of the movable conveyor.
The invention also considers a grinder, wherein the subframe cooperates with a vertically adjustable abutment member. In such a grinder the minimum width of the distance between the upper and lower conveyors is limited to an adjustable value. At the same time the movable conveyor is free to move in vertical direction when cooperating with waste material pieces of greater height.
The grinder may be provided with a support plate to supports the upper run of at least one of the conveyors. In such a grinder the upper runs of the respective conveyors are vertically supported and run at a predetermined height.
Furthermore a grinder is proposed, wherein at least part of the support plate is made from material cooperating with the associated transport element under low friction. In such a conveyor the lower sides of the transport elements can move across the associated support plate under small friction.
The invention further proposes a grinder, wherein pressure rollers act on the lower run of the upper conveyor, said pressure rollers being biassed by spring elements. This construction allows for increased engaging forces between the two conveyors and the waste material to be comminuted.
The invention furthermore proposes a grinder, wherein at least part of the spring elements comprise gas springs. In such a grinder the force exerted by the springs onto the transport element biassed thereby can be easily adjusted by varying the pressure in the gas spring.
The invention also proposes a grinder, wherein independent identical drive units are provided for the upper and lower conveyors. In such a grinder there is no need for a positive mechanical couppling between the two conveyors. Also the conveyors can run at somewhat different speed if such is required by the geometry of the arrangement of the two conveyors (upper conveyor parallel to the lower conveyor or inclined with respect to the lower conveyor) or by load requirements.
A grinder is preferred, wherein a load sensor cooperates with a motor driving the grinding rotor and wherein the drive units associated to the upper and lower conveyors are energized in accordance with the signal output from said load sensor. In such a conveyor the waste material feed means are automatically stopped when the grinding rotor needs too torque to comminute the waste material in its vicinity. The waste material transport means are automatically restarted, when the grinding rotor is ready to comminute further material.
Further improvements of the invention relate to the grinding rotor running at a speed of 120 to 240 rpm or preferably between 160 and 200 rpm. Operation of the grinding rotor at such rpms is particularly advantageous in connection with alongate waste material pieces consisting of wood, chip board and the like.